Plaskett, John Stanley (1865–1941)

John Plaskett was a Canadian astronomer and mechanical engineer who, in 1918, became director of the newly established Dominion Astrophysical Observatory (DAO) in British Columbia, for which he had organized the design, construction, and installation of a new 72-inch (1.8-meter) reflecting telescope. Plaskett's field of research was spectroscopy, in particular the measurement of radial velocities of celestial bodies, i.e., their velocities along the line of sight, from the shift in their spectral lines. Using the 72-inch reflector and a highly sensitive spectrograph which he had also designed, many spectroscopic binary systems were discovered. In 1922, Plaskett identified an extremely massive star as a binary, now known as Plaskett's Star. In 1927 he provided confirmatory evidence for the theory of galactic rotation put forward by Bertil Lindblad and Jan Oort. By 1928 Plaskett, in collaboration with Joseph Pearce, had obtained evidence for the hypothesis formulated by Arthur Eddington in 1926 that interstellar matter was widely distributed throughout the Galaxy; their discovery that interstellar absorption lines, mainly of calcium, took part in the galactic rotation, showed that interstellar matter was not confined to separate star clusters. Although this result was first announced by Otto Struve in 1929, Plaskett felt he had priority and was convinced that Struve had obtained his results from him. He retired from the DAO in 1935.

John Stanley Plaskett